rust

问题 This question already has an answer here : Differences in Type inference for closures and functions in rust (1 answer) Closed 2 years ago . The return type of a block is inferred. fn main() { let x = { 5 }; println!("{}", x); } But when I give the block a name, I have to specify a type. fn five() -> i32 { 5 } fn main() { let x = five(); println!("{}", x); } How can I avoid selecting a type? 回答1: You cannot. Rust explicitly prohibits this by design. However, for large and complex return types,

问题 The std::error::Error trait is transiting to a new design. Noticeably its cause method: fn cause(&self) -> Option<&dyn Error> is deprecated and to be replaced by: fn source(&self) -> Option<&(dyn Error + 'static)> Besides the name, the only change is that the new method returns 'static . The reason given by fix error RFC is: The problem with the existing cause API is that the error it returns is not 'static . This means it is not possible to downcast the error trait object, because

问题 The std::error::Error trait is transiting to a new design. Noticeably its cause method: fn cause(&self) -> Option<&dyn Error> is deprecated and to be replaced by: fn source(&self) -> Option<&(dyn Error + 'static)> Besides the name, the only change is that the new method returns 'static . The reason given by fix error RFC is: The problem with the existing cause API is that the error it returns is not 'static . This means it is not possible to downcast the error trait object, because

问题 I'm writing a Rust interface to a small C library, which has headers spread in a few locations. It's not a system library, and is normally used by some executables in the same package; I'm currently including it as a git submodule in my Cargo project. Building the library seems to be pretty easy; I've opted to use the gcc crate from build.rs : gcc::Config::new() .file("external/foo/dir1/file1.c") .file("external/foo/dir2/file2.c") .include("external/foo/dir1/") .include("external/foo/dir2/")

问题 I am taking my first steps on Actix-Web. But this closure causes me errors #[derive(Deserialize, Serialize, Debug, Copy, Clone)] pub struct PaginationQuery { pub limit: Option<u32>, pub offset: Option<u32>, } pub fn get_all_trainings_2( query: web::Query<PaginationQuery>, pool: web::Data<Pool>, ) -> impl Future<Item = HttpResponse, Error = Error> { let mut pagination = query.0; // Thread Blocking web::block(move || database::get_exercises(pool, pagination)).then(|res| { match res { Ok(

问题 I am taking my first steps on Actix-Web. But this closure causes me errors #[derive(Deserialize, Serialize, Debug, Copy, Clone)] pub struct PaginationQuery { pub limit: Option<u32>, pub offset: Option<u32>, } pub fn get_all_trainings_2( query: web::Query<PaginationQuery>, pool: web::Data<Pool>, ) -> impl Future<Item = HttpResponse, Error = Error> { let mut pagination = query.0; // Thread Blocking web::block(move || database::get_exercises(pool, pagination)).then(|res| { match res { Ok(

问题 If I define a dependency like foo = { version = "1.0.0", optional = true } , will it be available when I do "cargo run"? Can I check if it is enabled in the code? if cfg!(feature = "foo") {} Doesn't seem to be working, like the feature is missing all the time. 回答1: Moving answer to 60258216 here: Optional dependencies do double as features: https://stackoverflow.com/a/39759592/8182118 They will not be enabled by default unless they're listed in the default feature, though you can enable the

问题 If I define a dependency like foo = { version = "1.0.0", optional = true } , will it be available when I do "cargo run"? Can I check if it is enabled in the code? if cfg!(feature = "foo") {} Doesn't seem to be working, like the feature is missing all the time. 回答1: Moving answer to 60258216 here: Optional dependencies do double as features: https://stackoverflow.com/a/39759592/8182118 They will not be enabled by default unless they're listed in the default feature, though you can enable the

问题 For an exercise I'm doing for exercism (the minesweeper task), I need to convert an usize to a char in order to insert it into a std::string::String . To describe the problem in minimal lines of code: let mut s = String::from(" "); let mine_count: usize = 5; // This is returned from a method and will be a value between 1 and 8. s.insert(0, _______); // So I get: "5 " at the underscores I do: The way I'm currently doing this as: mine_count.to_string().chars().nth(0).unwrap(); // For example:

问题 I'm setting up a Rust server with Rocket and I'm trying to use it with a JWT library. They use different versions of the *ring* crate and I get an error during cargo build : error: multiple packages link to native library `ring-asm`, but a native library can be linked only once package `ring v0.12.1` ... which is depended on by `jsonwebtoken v4.0.1` ... which is depended on by `auther v0.1.0 (file:///home/drpytho/x/downloadble/auther)` links to native library `ring-asm` package `ring v0.11.0`